Lumber Choices for Fence Posts and Rails

      A discussion comparing various wood species with pressure treated lumber for use in building fences. March 28, 2012

I'm not sure which is best for fence boards (1X6X16). I'd like to use white oak since it would be cheaper for me to cut with my mill. But I do want it to last. I'm in NC and I've heard different stories - good and bad - about using oak. Has anyone got experience with oak fencing in my area? I do have a nail gun. I've heard it's hard to nail. Also when to cut the oak trees down, if it makes any difference?

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
There is no difference in the time of year a tree is cut. Wet oak is easy to nail with a gun. White oak - heartwood only! - is fairly decay resistant (except for a few species like chestnut white oak). Pressure treated will give you much longer life overall, especially when in contact with the soil. But above ground for a fence board, white oak is suitable.

From the original questioner:
Thanks Gene. I'm planning on using 4X4 cedar for my posts in the ground and white oak or treated pine for my boards.

From contributor W:
I would use the pressure treated in the ground.

From Professor Gene Wengert, forum technical advisor:
Cedar posts, with today's cedar and the large amount of sapwood (white color), would also make me use treated for the posts. In fact, that is what I did already.

From contributor A:
Another way to help the post last longer in the ground is to burn the end. Build a fire till it burns down to a good bed of coals, then lay the end of the post in the coals till the bottom part is blackened. ERC is good so long as you have lots of red in the bottom.

From Professor Gene Wengert, forum technical advisor:
The idea of burning is good indeed. In fact, in the early surveys of the western US, the survey markers were pieces of non-native wood that were burned prior to burying. The survey notes included the species. So, for 100 years or so, when there was a survey question, these pieces of wood were found, identified as to the species, and, if the correct species, used as legal evidence on the location of a survey location.

From contributor B:
I know white oak works for outdoor projects… What about hickory, ash or locust?

From contributor A:
Other than tool handles, I would not use hickory or ash. They just do not hold up well. Both honey and black locust do well, with black being one of the best.

One thing you have to remember is in some places like Montana they get by putting pine poles outside where they do not get much rain or have termites. Put a pine pole out in Arkansas and by the end of the year you will have mush laying on the ground.

From Professor Gene Wengert, forum technical advisor:
I agree. Black is really good (heartwood only again). However, it is so hard to work, including nail driving, that it is usually not used.

From contributor S:
Black locust is probably better than pressure treated for posts. There is a lot of old fencing in the area where I live and the black locust posts are about 40 years old. Many of them are still completely solid.

From Professor Gene Wengert, forum technical advisor:
Pressure treated (for ground contact) will last 100 years or more in wet environments, unless it is damaged mechanically. That is why power poles will be pressure treated... The cost to replace a failed pole is enormous.

Pressure treated wood posts and poles are also in various shapes… 3x3, 4x4, 4x6, rounds with a flat spot where the fence boards will attach, or perfectly round of various diameters. Each piece of pressure treated can be identical in shape and size.

Black locust must have the sapwood removed prior to installation (or at least tolerate its removal by decay fungi and/or insects when in the ground). The shape will vary from piece to piece. In a wet environment, it will have trouble lasting for a century.

Contributor S, where are you located? Also, when you say many are solid after 40 years, how many are not?

When building a fence, we need to ask ourselves what will happen if a post fails. If it just a yard fence, not much damage is likely. If it is a fence holding expensive animals, a failed post could be very serious. When the long life is critical and the expense of failure is high, then always use properly pressure treated wood.

From contributor S:
I'm in southwestern PA. I would say that 90% are so solid it is difficult to remove them. On the other hand, I have seen fences made of pressure treated lumber that start rotting below the ground after only a few years. Obviously, there is a discrepancy due to the way the pressure treating is done. A lot of commercially available pressure treated wood, especially larger sizes 6 x 6 and up, is not well impregnated and the core is sometimes not treated.

From Professor Gene Wengert, forum technical advisor:
There are two basic levels of pressure treatment... above ground and below ground. There is a third level that is called treating to refusal which means you try and get as much chemical in as possible. However, if the wood has not been dried much, you will not get much chemical in. In one case in GA, the wood was treated with some oil that had a green color added. Properly done and with an appropriate quality sticker or stamp, you will have a long life indeed from the wood.

From contributor K:
I built the fence across the front of my parking lot in 1983 using white oak. After 28 years, it hasn't rotted. I cut off all the sapwood before installing. The climate in Arkansas is probably similar to yours in NC.

If you use wide boards, don't nail out near the edges. The seasonal changes will be harder on your nails or fasteners. I normally have half the width between fasteners, with 1/4 on each side, then angle them in toward the middle. I think this reduces some of the breathing out of the fasteners.

From Professor Gene Wengert, forum technical advisor:
Contributor K, did you use white oak for the posts too? Are they buried in concrete or just in a hole in the dirt?

From contributor K:
No, I used railroad ties for posts, and pressure treated pine 4 x 4 rails to attach the oak to. It is 10' high. I have had to replace some of the tie posts, which were used. I tried to buy new, but couldn't find a supplier back then that would sell to me.

From contributor T:
I saw a lot of telephone poles for fence posts and rails and also pole barn lumber. Some poles aren't saturated as much as others. When I find one that is soaked all the way through the middle, I try to make a 4x4, 6x6, or 4x6 from it. It makes a nice looking fence that will last for years. It's a lot cheaper than buying pressure treated from a lumberyard.

From contributor R:
4''x6''x8' landscape timbers at Home Depot are 2 dollars each. I couldn't make them at that price if you gave me the wood for free.

From Professor Gene Wengert, forum technical advisor:
Used RR ties (7x9x8-1/2') are also sold at fairly low prices, but they are quite heavy (each 150 pounds or more), so many people cannot haul and handle them in a home landscaping effort.

In any case, be very careful when processing treated wood. The sawdust can be both a human health issue and an environmental issue if one is not careful.

From the original questioner:
I'm planning on using red cedar for my posts and the white oak for my boards. I'm going to cut the oak board 5/4 for extra support. I have the cedar on hand but will have to look for some oaks. I have some real nice ones but really don't want to cut them.

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